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SCI 102 Evolution ESRA BATTALOĞLU Major themes in Biology Unity and diversity among organisms Unity : the following and many other properties are shared by all organisms; cell is the basic unit Have DNA as genetic material Life requires energy transfer Structure and function are correlated, … Core theme in Biology Diversity: 1.8 million species have been identified and named Estimated number of species is 10-100 million Along with a vast diversity we find many shared features Evolution can explain both unity and diversity Core theme of biology is EVOLUTION!!! Observations of Charles Darwin Org’s are strikingly well suited to their env. They share many characteristics of life (unity) There is a rich diversity among org’s Darwin’s voyage with Beagle Darwin in 1840, after his return from the voyage HMS Beagle in port Great Britain NORTH AMERICA The Galápagos Islands ATLANTIC OCEAN Pinta Santiago 0 20 40 Kilometers Daphne Islands Santa Santa Cruz San Fe Cristobal Florenza SOUTH AMERICA Equator Pinzón Isabela AFRICA PACIFIC OCEAN Genovesa Marchena Fernandina EUROPE Española Chile PACIFIC OCEAN Equator Brazil Cape of Good Hope Argentina Cape Horn Malay Archipelago PACIFIC OCEAN AUSTRALIA Tasmania New Zealand Natural Selection: A Summary Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species Natural selection increases the match between organisms and their environment over time It is the populations not the individuals that evolve If individuals are genetically identical (no inherited variations in the population), evolution cannot take place. A trait favorable in one place or time may be useless or damaging in other places and time. Thus, in natural selection which traits are favored depends on where and when the species live and mate. Nature selects the traits natural selection Cumulative effects of natural selection Natural selection over years cause ancestral species to change and give rise to descendant species Ex: due to geographical isolation Ex: 14 species of finches identified by Darwin in Galapagos islands is an example of speciation due to geographical isolation (Galapagos islands are volcanic islands in Pacific ocean close to South America) Adaptations of finches in Galapagos islands (a) Cactus-eater (b) Insect-eater (c) Seed-eater Source of heritable variation: Mutations Mutations are changes in the DNA sequence of an organism. They give rise to new forms of a given gene alleles Ex: Gene 1; encoding for protein A Allele a of gene 1: encoded protein functions with 80% efficiency Allele b of gene 1: encoded protein functions with 40% efficiency Alleles are different forms of a gene Mutations may have neutral, harmful or beneficial effects on the gene and the encoded product by that gene. Mutations Mutations occur due to; Mistakes during copying of DNA in the cell (DNA replication) before the cell splits into two Collisions of DNA with other molecules Damage from radiation and chemical agents Mutations occur randomly Mutations do not occur when the organism needs them, Instead: They occur randomly at any time and not directed toward a goal Ex: bacteria accumulate mutations that confers resistance to antibiotics By using these antibiotics in an uncontrolled way, the bacteria having resistance to that antibiotic are selected and survive. The antibiotic sensitive ones die. The mutation that confers resistance to bacteria does not appear when we take the antibiotic, it is already present in the bacterial population. Mechanisms of Evolution Mutations: raw material on which evolution can work Natural selection: organisms best suited to the environment survive and reproduce better than individuals less suited to the environment. Genetic drift: chance events that cause some individuals to leave more offspring than others Gene flow: introduction of alleles to a population due to an exchange of alleles between different populations Genetic Drift Chance events that can cause some individuals to leave more offspring than others Genetic drift and natural selection cause random fluctuations in the genetic make-up of populations over time They act together to produce evolutionary change However, in small populations the effect of genetic drift can be a disadvantage for the species Genetic Drift • It can cause loss of an allele even in two generations • It leads to fixation of only one allele in the population that can be neutral, beneficial, or harmful Genetic drift in small populations In large populations its effect can be overcome by natural selection and other evolutionary mechanisms. It is important to know about genetic drift for preservation of rare species African cheetah Genetic bottleneck Small population genetic drift loss of genetic variation fixation of harmful alleles Extinction of species A population experiencing such a situation is said to be in ‘genetic bottleneck’. Ex: African cheetah Ex: Florida panthers: males have low sperm counts due to a harmful mutation that is fixed. 30-50 panthers increased to 100s Gene Flow When individuals move from one population to the other they may introduce new alleles to the population they moved. (As if there occurred a mutation in the new population) Ex: an allele that confers resistance for a pesticide in mosquito spread over three continents –Asia, Europe and North America The mutation is advantageous for the mosquito but it counteract the effects of natural selection. Gene Flow How gene flow counteracts the effects of natural selection. If populations are isolated from each other natural selection favors accumulation of mutations and species isolation. However, gene flow among isolated populations keep their genetic make-up similar. They may remain genetically similar despite the effects of natural selection. Evidence for evolution Surveys showed that about 50% of adults in our country do not believe that evolution is at work and humans evolved from earlier species of animals. Evolution has been defined for 150 years and evidence is very strong. For scientists the issue is not whether evolution has occurred but is how evolution works. Evidence for evolution Darwin could not convince some of other scientists at his time in natural selection because mechanisms of inheritance was not known. Lines of evidence There are four types of data that document the pattern of evolution; Direct observations Homology The fossil record Biogeography The Evolution of Drug-Resistant Bacteria The bacterium Staphylococcus aureus is commonly found on people One strain, methicillin-resistant S. aureus (MRSA) is a dangerous pathogen Resistance to penicillin evolved in S. aureus by 1945, two years after it was first widely used Resistance to methicillin evolved in S. aureus by 1961, two years after it was first widely used MRSA strains are now resistant to many antibiotics Evidence of evolutionary history: homology Evolutionary relationships among organisms can be determined by their anatomical features. Ex: bat wing and human arm; remarkable similarity in limb structure with different function human cat whale bat Evidence of evolutionary history: homology Homology is similarity resulting from common ancestry Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor Ex: Whale embryos with teeth (disappear in adult) Ex: Human embryos have gill pouches (develop into ear bones) Fossil records: Whales evolved from organisms with teeth. A group of fish first amphibians : a group of amphibians first reptiles: a group of reptiles first mammals: a group of mammals human Fossils They are preserved remains or impressions of formerly living organisms. Document extinction of species How descendants of species changed overtime How new organisms have evolved from ancestral organisms How environments changed over time (Fossils of whales in Sahara desert; fossils of trees and tropical marine organisms in Antarctica) Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) †Moeritherium †Barytherium †Deinotherium †Mammut †Platybelodon †Stegodon †Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) 60 34 24 5.5 2104 0 Millions of years ago Years ago In 32 MY, 7 elephant species became extinct. Thus, there is no species to fill in the gap between elephants and their nearest relatives (manatees). 99% of species are now extinct!!! Fossils Fossil records have many gaps due to several reasons: Organisms decompose very rapidly after death May be destroyed by geographical processes (erosion, heat, pressure) Difficult to find Each year new discoveries fill in these gaps. Fossils Fossil records show five mass extinctions of species. Each caused about 50% of species to be lost After each mass extinction surviving groups diversified, caused bursts of evolution Each of these bursts in evolution lasted about 10 million years. Ex: dinosaurs went extinct 65 mya, mammals diversified in size and ecological role, otherwise human probably would not exist. Sixth mass extinction can be the one that is caused by human Evidence of evolutionary history DNA sequence/ protein analyses: the higher the homology between the DNA sequence the more closer the species in evolutionary tree. If organisms were not related to one other by a common ancestor, there would be no reason to expect a degree of similarity in DNA and proteins. Evidence of evolutionary history These different sources of information (anatomy and DNA sequence) are usually the same. Independent lines of evidence yield the same result. Evolutionary tree Branch point Lungfishes Digit-bearing limbs Amnion Lizards and snakes 3 4 Homologous characteristic Amniotes Mammals 2 Crocodiles Ostriches 6 Feathers Hawks and other birds Birds 5 Tetrapods Amphibians 1 Evidence for evolution: Biogeography Biogeography, the scientific study of the geographic distribution of species, provides evidence of evolution. Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift. An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved. Evidence for evolution: Biogeography Continental drift Earth’s continents move over time. South America and Africa move away from each other (3cm/year) Ex: today’s lungfish is found only in Australia, its ancestors lived in the single continent of earth (Pangaea) and their fossils are found on all continents except Antarctica. Ex: today’s modern horse first evolved in North America, oldest fossils are found in North America. The land bridge between North and South America formed 3 mya. Fossils of ancestors in South America is less than 3 million years old. Genetic changes within species The tremendous variation produced by human within dogs and ornamental flowers Breeding organisms only with certain characteristics artificial selection Natural selection can produce similar evolutionary changes What Is Theoretical About Darwin’s View of Life? In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions Ongoing research adds to our understanding of evolution Human Evolution Human beings are animals; Mammals primates hominid As other animals we have body hair and mammary glands As primates we have; Flexible shoulder and elbow joints Five functional fingers and toes Thumbs that are opposable Flat nails (not claws) Brains large in relation to our body size Who are we? Where do we come from? Genetic analyses and fossil discoveries lead to understanding our evolution Chimps and human diverged about 5-7 mya Diverged from gorilla about 7-8 mys Diverged from the lineage of orangutans about 12-16 mya DNA analyses results The difference between chimp and human DNA is about 1%. In some regions our DNA is closer to that of gorillas. In still other regions chimps and gorilla are more closely related to each other than to human. We are Apes We are not just closely related to APES but we are APES. Characteristics shared by apes; Use of tools Capacity for symbolic language Sense of self-awareness HOMINIDS (pr0-human) Primates are thought to have originated 80-85 mya from small mammals (fossils date 56 mya). They were eating insects and living in trees. Over time they diversified giving rise to hominids. Hominids; Have large brain An upright walking posture Complex tool making behaviors First big step Tool making and intelligence are secondary changes in evolutionary sense. The first big step in human evolution was a shift from being quadrupedal (moving on four legs) to being bipedal (walking upright on two legs). It was a change occured long before hominids evolved large brains. Standing up Standing up freed our hominid hands to eventually allow for tool use. Tool use led to greater success in hunting or otherwise acquiring meat in the diet. A diet rich in meat provided more of the basic biochemical building blocks needed for brain development. Someone, at some point, learned how to use fire. Someone started talking. Someone started writing. First big step It is accompanied by skeletal changes; including loss of opposable toes (the big toe is opposable in all primates except humans). Loss of it on the trees was a disadvange but on the ground it was an advantage. Thus, evolution to upright posture is linked to a switch from life in the trees to life on the ground. (Probably occured 8-5 mya) Earliest known hominids Sahelanthropus tchadensis (6-7 my old skull found in 2002) Ardipithecus ramidus (5.8-4.4 mya) Australopithecus species (4.2-3.0 my old) ARDI Female Ardipithecus ramidus Found in Etopia in 1992 The fossil is 4.4 my old LUCY Female Australopithecus afarensis Found in 1974 in Etopia 3.2 my old Small skull Bipedal Evidence for: bipedalism preceeded increase in brain size Earliest known hominids The last two might have upright posture; the size of brains were relatively small; and their skull and teeth were more similar to other apes. Evolution of genus Homo; Homo habilis Oldest homo fossils were found in Africa; date to 2.4 mya Homo habilis (1.9-1.6 mya) Their fossils resemble to those of Australopithecus africans In their most recent fossils the face is not pulled forward and the skull is more rounded. Homo erectus Homo erectus evolved from H. Habilis (from which sub-species is not known) H. erectus or an earlier form had migrated from Africa. Homo fossils Have been found in Java, Georgia (central Asia), China (dating 1.9-1.7 mya) H. habilis lived near Indonesian islands 1 my -25.000 years ago. H. sapiens live in the same regions from 60.000 years ago to present. There are more species of homo than thought before and several of them existed in same places and times. Homo sapiens Originated between 400.000 – 130.000 years ago. Some of these are lost 30.000 years ago. Early species of archaic H. sapiens gave rise to both; Neandertals Modern humans Neandertals lived from 230.000 to 30.000 ya. Modern human fossils; Oldest fossils date to 130.000 y in Africa 115.000 y in Israel 60.000 y in China 56.000 y in Australia 18.000-13.000 y in America Origin of human The two hypothesis; Out of Africa hypothesis; human evolved 200.000 ya in Africa from unknown archaic H. sapiens populations. Than, spread to the world, completely replacing all of the H. sapiens populations (H. erectus, Neandertals, H. floresiensis) Origin of human Multiregional hypothesis; proposed that modern humans evolved over time from H. erectus located throughout the world. Regional differences developed early but gene flow caused them to remain as a single species. Origin of human DNA analyses results support out of africa hypothesis. However, ‘complete replacement’ is questionable. DNA analyses show that genes from archaic populations outside Africa might have contributed to genetic make-up of modern humans. Our evolutionary future Genetic drift was the likely evolutionary mechanism in older ages. The populations were small and isolated, without gene flow. Now that the human populations are large and not isolated, genetic drift has probably not have a major role. Instead, gene flow plays a critical role and may reduce differences among populations over time. Our evolutionary future Natural selection does not act in the same way as in older ages but it is still at work Ex: infectious diseases apply a pressure on populations Ex: resistance to malaria increased in frequency so rapidly that it can be best explained by natural selection. Effect of human on evolution Cut down forests Drain wetlands Plow grassland Add chemicals to air, water, soil Kill large predators They cause profound changes in env. where species live. Species evolve in response to env. The changes we make to those env.s alter the course of evolution in many species. Effect of human on evolution We should understand how we affect evolution. Based on current forest breakdown scientists estimate that all the world’s tropical forests will be cut down in the next 50 years. Since over 50% of world’s species live in tropical forests we may cause sixth mass extinction. If that happens, course of evolution will be altered and history of life on Earth may change forever. Recovery requires millions of years. BIODIVERSITY